1. Field of the Invention
The present invention relates to a spectacle lens frame shape measuring apparatus measuring the shape of a lens (a lens frame or a frame) of spectacles and specifically relates to an improvement of the measuring apparatus in which upper holding pins hold upper rims of spectacle lens frames at different positions in a right-left direction from positions at which lower holding pins hold lower rims thereof.
2. Description of the Related Art
For processing lenses to be attached to a spectacle lens frame, it is necessary to previously measure the shape of the spectacle lens frame. As an apparatus for measuring the shape of the spectacle lens frame, a spectacle lens frame shape measuring apparatus is known.
Such a spectacle lens frame shape measuring apparatus includes: a holding device holding upper and lower rims of spectacle lens frames with holding pins; and a probe moving (rotating as well as advancing and retracting in a radial direction) along the entire circumference of the lens frame while abutting on the lens fitting grooves of the spectacle lens frames held by the holding device.
For example, Japanese Unexamined Patent Application Publication Nos. H2-214810 (reference numbers 18B, 18C, and 18D in FIG. 2) and H4-93163 (reference numbers 2114a to 2114c and 2214a to 2214c in FIGS. 3-1 and 3-5) show the following configuration for measurement of spectacle lens frames. In the configuration, a linear section of the upper rim of each spectacle lens frame (a section extending in a crosswise direction (in a right-left direction of the spectacle frame)) is longer than a linear section of the lower rim thereof. Specifically, in order to provide stable hold with the upper holding pins holding the upper rims and the lower holding pins holding the lower rims for such a spectacle frame, the upper holding pins are placed at different positions from those of the lower holding pins in the right-left direction (each of the upper holding pins is not positioned on an extension of the corresponding lower holding pin).
When the upper rim is longer than the lower rim, the distance between the upper holding pin of the left lens frame and the upper holding pin of the right lens frame is set longer than the distance between the lower holding pin of the left lens frame and the lower holding pin of the right lens frame. The lens frames can be therefore stably held even when subjected to load by the probe coming into contact with the lens frames.
The same goes when the upper rim is shorter than the lower rim.
In recent years, spectacle lens frames which are highly curved and cambered so as to fit a spectacle wearer's face (having a large curved angle (rising angle)) have appeared, such as sunglasses for sport.
At measurement of the lens frame shape of a spectacle frame having lens frames with such a large curved angle (for example, not less than 15 degrees), the probe moves by a larger amount in regions of the lens frames closer to right and left outer edges and is more likely to be disengaged from the lens fitting grooves, or the lens frames are more likely to be deformed. Accordingly, proper measurement values may not be obtained.
Accordingly, a measuring apparatus including a holding device swinging mechanism which swings holder pins around a virtual axis is proposed. (International Publication No. WO2008-97564 (FIG. 7, etc.)). In the measuring apparatus, the holding device is swung by the holding device swinging mechanism so that the target lens frames may be placed at a substantially uniform attitude with respect to the probe.
Note that, each of the upper holding pins in International Publication We. WO2008-97564 is placed on an extension of the corresponding lower holding pin.
As shown in FIG. 35, even in the case of measuring the shape of spectacle lens frames RF and LF with a large curved angle as described above, in the light of stable holding of the spectacle lens frames RF and LF, it is preferable to place upper holding pins 3b4 holding upper rims RF1 and LF1 at positions which are not on extensions of lower holding pins 3b6 holding lower rims RF2 and LF2, respectively.
Meanwhile, for example, a spectacle lens frame shape measuring apparatus in which a distance L1 between the right and left upper holding pins 3b4 and 3b4 is not equal to a distance L2 between the right and left lower holding pine 3b6 and 3b6 (L1≠L2), similar to the conventional spectacle lens frame shape measuring apparatus in which the distance L1 is set equal to the distance L2 (L1=L2), is configured so that the upper holding pins 3b4 and 3b4 may hold the lens frames RF and LF at the same height as the lower holding pins 3b6 and 3b6 hold the lens frames RF and LF.
In other words, in the lens frames RF and LF held by the upper and lower holding pins 3b4, 3b4, 3b6, and 3b6, the upper rims RF1 and LF1 and the lower rims RF2 and LF2 are at the same height.
In the spectacle lens frames RF and LF held by the spectacle lens frame shape measuring apparatus configured as described above, if the distance L1 between the right and left upper holding pins 3b4 and 3b4 is longer than the distance L2 between the right and left lower holding pins 3b6 and 3b6 (L1>L2) as shown in FIG. 35, for example, the upper holding pins 3b4 and 3b4 hold portions on the outside of the lower holding pins 3b6 and 3b6 in the right-left direction.
At this time, when the spectacle lens frames RF and LF have a large curved angle (for example, not less than 15 degrees), as shown in FIG. 36, the height of the frames from a reference surface h0 increases toward outsides in the right-left direction corresponding to the inclination of the curved angle. Accordingly, as shown in FIG. 36 and FIG. 37A showing the spectacle lens frames RF and LF not yet held, the portions of the upper rims RF1 and LF1 held by the upper holding pins 3b4 and 3b4 are higher by Δh than the portions of the lower rims RF2 and LF2 held by the lower holding pins 3b6 and 3b6 (h1>h2).
It should be noted that the aforementioned height difference between the upper holding pins 3b4 and 3b4 and the lower holding pins 3b6 and 3b6 is for the sake of explanatory convenience. In practice, the upper holding pins 3b4 and 3b4 and lower holding pins 3b6 and 3b6 are fixed at the same height (for example, at a height h2) and cannot move in a height direction. In other words, FIG. 37A is a view assuming the case of the conventional spectacle lens frame shape measuring apparatus in which the upper holding pins 3b4 and 3b4 are arranged on respective extensions of the lower holding pins 3b6 and 3b6.
However, the upper holding pins 3b4 and 3b4 and lower holding pins 3b6 and 3b6 are set at the same height h2 in a state where the spectacle lens frames RF and LF are held as shown in FIG. 37B. Accordingly, the frames are held with the upper rims RF1 and LF1 pressed down (to an inclined position) by the original height difference Δh (=h1−h2) according to the curved angle and the distance difference between the upper and lower holding pins (ΔL=L1−L2).
When the spectacle lens frames RF and LF are swung by the holding device swinging mechanism for measurement of the spectacle lens frame shape with the upper rims RF1 and LF1 inclined to a position indicated by solid lines in FIG. 38, instead of the position indicated by two-dot chain lines in the same drawing where the spectacle lens frames RF and LF should be originally hold, because of the influence of the inclination of the upper rims RF1 and LF1, the result of the measurement with the upper rims RF1 and LF1 inclined as indicated by solid lines of FIGS. 39A and 39B is shifted by an axial shift amount or angle θ3 from the result of measurement which would be obtained with the upper rims RF1 and LF1 not inclined as indicated by two-dot chain lines of the same drawings.
Accordingly, the shapes of the spectacle lens frames RF and LF may not be obtained with high accuracy.
When the distance L1 between the right and left upper holding pins 3b4 and 3b4 is shorter than the distance L2 between the right and left lower holding pins 3b6 and 3b6 (L1<L2), the upper holding pins 3b4 and 3b4 hold the spectacle lens frames RF and LF on the inside of the lower holding pins 3b6 and 3b6 in the right-left direction. In the case where the spectacle lens frames RF and LF have a large curved angle, the portions of the upper rims RF1 and LF1 held by the upper holding pins 3b4 and 3b4 are lower than the portions of the lower rims RF2 and LF2 held by the lower holding pins 3b6 and 3b6. If the upper holding pins 3b4 and 3b4 are set at the same height as the lower holding pins 3b6 and 3b6 (at the height h2 when the lower holding pins 3b6 and 3b6 are taken as a reference), the spectacle lens frames RF and LF are held with the upper rims RF1 and LF1 pressed up. Accordingly, this case also results in an axial shift with respect to the result of measurement which would be obtained with the upper rims RF1 and LF1 not inclined.
Herein, the axial shift amount or angle θ3 occurs in the following manner. When the spectacle lens frames RF and LF are held while being inclined or the spectacle lens frames RF and LF are swung to the right or left while being inclined, the shape of the spectacle lens frames RF and LF projected onto a horizontal plane are twisted at the inclined right and left end portions. Accordingly, the shapes of the spectacle lens frames RF and LF calculated based on the measured shapes of the spectacle lens frames are tilted with respect to those which would be obtained with the not-inclined frames at the deviation angle θ3 with a geometrical central position C1′ of the spectacle lens frame indicated by two-dot chain lines of FIG. 39A being shifted from an original geometrical central position C1 of the spectacle lens frame not inclined (solid lines). Alternatively, as shown in FIG. 39B, the calculated shapes of the spectacle lens frames RF and LF are tilted at the deviation angle θ3 with the geometrical central position C1′ of the spectacle lens frame indicated by the two-dot chain lines being substantially coincident with the original geometrical central position C1 of the not-inclined spectacle lens frame (the solid lines). This tilt angle θ3 results in an axial shift amount.
This axial shift will adversely affect the measurement result of the shape of a normal spectacle lens frame. To be specific, when the shape of each spectacle lens frame obtained by measurement is tilted at the deviation angle θ3, FPD, which is a distance between geometrical centers of the right and left spectacle lens frames, differs from an original FPD of spectacle lens frames not inclined. This makes it impossible to accurately grinding spectacle lenses fit to the spectacle lens frames.